1. Field of the Invention
The present invention relates to an image formation device, and more particularly to an image formation device that forms an image on the surface of a disc-shaped recording medium.
2. Description of the Related Art
Various types of disc-shaped recording media, such as a CD, CD-R, CD-RW, DVD, and DVD-RAM, are known as recording media for recording electronic data such as images, videos, music, and documents. When various types of data are written for recording on any of those disc-shaped recording media, the information indicating the recorded content, for example, a title, is sometimes recorded on the surface of the disc-shaped recording medium to allow the user to visually recognize the content recorded on the disc-shaped recording medium.
In this case, the user usually writes the information directly on the surface of a disc-shaped recording medium with a writing implement. In some other case, the user prints the recording information on a separately prepared label paper with a printer and pastes this label paper on the surface of the disc-shaped recording medium.
There are the following problems with the methods described above. That is, when the user writes the information directly on the surface of a disc-shaped recording medium, there is a possibility that the information recording surface of the recording medium is damaged by a writing implement. When the recording information is recorded on label paper with a printer, the printer is separately required.
To solve those problems, an optical disc drive is proposed that uses a laser beam to form an image on the label side to eliminate the need for writing the information with a writing implement and for printing the information with a printer (Patent Document 1).
According to the printer disclosed in this document, an optical disc on which a visible-light characteristic change layer made of a light-sensitive material and a heat-sensitive material is formed in a position that can be seen from the label side, is set on the turn table of an optical disc drive with the label side facing the optical pickup. The optical disc and the optical pickup are relatively moved along the surface of the optical disc and, in synchronization with this movement, the power of the laser beam projected from the optical pickup is modulated according to image data such as characters and pictures to be formed into images, and the modulated beam is focused on the visible-light characteristic change layer. Focusing a laser beam in this way changes the visible-light characteristic of the visible-light characteristic change layer and, as a result, forms an image.
The printer described in Document 1 given above performs the point-sequential scan operation, in which the optical disc and the optical pickup are relatively moved spirally or concentrically along the optical disc surface for printing, one pixel at a time, to form an image on the optical disc surface. The problem with this method is that it takes long.
In contrast to the point-sequential scan operation described above, another recording method is known in which the recording heads are arranged in all directions from the center of a disc-shaped recording medium to sequentially perform linear recording in synchronization with the rotation of the recording medium. A recording device is also proposed that uses inkjet recording heads as the linearly arranged recording heads to print an image on the disc medium surface while the recording medium is rotating (Patent Document 2).
In addition, to allow a label on an information recording medium to be rewritten, a label is also proposed that has a color development layer, which contains photo-chromic compounds as the color development material of the label, on its substrate to enable the light of a predetermined wavelength to be focused on this color development layer to change the hue (Patent Document 3).    [Patent Document 1] Japanese Patent Laid-Open Publication No. 2002-203321    [Patent Document 2] Japanese Patent Laid-Open Publication No. 2003-257153    [Patent Document 3] Japanese Patent Laid-Open Publication No. 2005-128453
On a disc-shaped recording medium, not only data is written on the information recording side to record information but also images such as pictures or characters are formed on the label side as described above.
Information is recorded, and images are formed, on a disc-shaped recording medium that is being rotated. At this time, information is recorded spirally or concentrically by relatively moving the disc-shaped recording medium and the optical pickup along the surface of the recording medium.
Known methods for recording information on a disc-shaped recording medium include the linear speed control method, angular speed control method, and linear/angular speed control method. For example, the linear speed control method refers to a method in which the rotation of a disc-shaped recording medium is controlled so that the linear speed in the center side of the disc is the same as the linear speed in the peripheral side, and the angular speed control method refers to a method in which the rotation of a disc-shaped recording medium is controlled so that the rotation angle of the disc is constant.
When a disc-shaped recording medium is rotated at a constant rotation speed, the recording density differs between the center side of the disc and the peripheral side because the linear speed of the disc differs between the center side and the peripheral side. On the other hand, the linear speed control method makes the recording medium recording density even by controlling the rotation of a disc-shaped recording medium so that the linear speed in the center side of the disc is the same as the linear speed in the peripheral side.
On the other hand, when an image is formed on the label side by the linearly-arranged recording heads, the recording heads are arranged along the radial direction of the disc-shaped recording medium and therefore the recording medium is usually controlled by the angular speed control method so that the rotation angle is constant. In this configuration, the image write processing for forming an image includes a process that is difficult to perform at a high speed.
In contrast, when data is written for recording information, the rotation speed is usually increased to reduce the recording time.
So, the image formation processing, which includes a process that is difficult to perform at a high speed, cannot be performed at the speed of the data write processing for information recording. This means that the information recording processing and the image formation processing are difficult to be performed at the same time and so they must be performed separately.
There is a need for reducing the time required for the image formation processing but, because the information recording processing and the image formation processing must be performed separately, it difficult to reduce the processing time for the image formation processing.
FIG. 7 is a diagram showing the relation between the processing time of image formation and that of the information recording described above. FIG. 7 shows the image formation processing in which light is focused on a recording medium on which the color development layer is provided. To form a multi-color image on a recording medium on which the color development layer containing photochromic compounds is provided, a light (ultraviolet radiation) of a predetermined wavelength is focused on the color development layer to develop the colors and, after that, the lights (multiple visible lights) of predetermined wavelengths different from that for color development are focused for color erasure. An image is drawn using the parts where colors are not erased and, after that, the image is fixed and stabilized.
Information recording and image formation are performed in one of the following sequences: image formation is performed after information recording as shown in FIG. 7A and information recording is performed after image formation as shown in FIG. 7B. In any of the sequences, it is difficult to reduce the time Tg required for image formation because information recording and image formation are performed individually.